European published patent specification EP-A-0,060,756 describes a lightning rod of this type, including a tip which is isolated from the ground, and which has a base connected to the ground via discharger means, said tip is also electrically connected to a generator of a direct positive voltage which is high enough to cause the ambient atmosphere at the end of the tip to be ionized (cornona discharge).
The zone of ionized air plasma formed in this way at the end of the tip has much higher electrical conductivity than ambient air, and thus facilitates lightning discharges towards the lightning rod, thereby improving its efficiency and its radius of action.
However, this increase in conductivity in the vicinity of the lightning rod tip has the effect of locally reducing the electric field, and it thereby inhibits the development of a brush discharge characteristic of a corona discharge from a tip raised to a positive potential, and brush discharge may constitute a favorable element in improving the efficiency of a lightning rod.
Further, the above-described device can only operate with negatively charged clouds (negative type lightning strikes) which corresponds to about 90% of cases in European countries, or even more if mountainous regions are ignored.